Batteries are routinely stored prior to and during use. Frequently they are discarded after storage while still having useful electrical power.
Battery testers for indicating battery capacity are known. Such devices are described in U.S. Pat. Nos. 4,737,020; 4,702,564; 4,702,563; 4,835,475; 4,835,476, etc. Such testers have also been incorporated into battery packaging. See U.S. Pat. No. 4,838,475.
These testers generally include a conductive layer in thermal contact with a temperature sensitive color indicator layer. When the ends of the conductive layer are contacted to battery terminals, electrical current flows, creating heat in the conductive layer. The heat causes a change in the indicator layer.
The usefulness of the above devices is extremely limited. They are also inconvenient to use. The tester must be carried as a separate item. This is aggravated in the case of testers incorporated into a package since the entire package must be carried separately.
In addition, current tester designs do not allow ease of operation on all cells. In most cases the tester is larger than the battery for which the tester is designed. This makes it difficult to maintain the terminals of the testers in contact with the batteries and achieve reproducible results because such testers are generally flexible.
Also the prior art battery testers cannot be used when the conductive circuits of the testers are in contact with battery housings. We have determined that the housings act as a heat sink diverting heat generated by the conductive layer away from the tester color indicating layer.